Elimination of film defects due to hydrogen evolution during cathodic electrodeposition

ABSTRACT

This invention is directed to a method for eliminating or reducing pinhole defects in cataphoretically deposited films without interfering with the electrolysis of water needed for electrodeposition. The method comprises decreasing the evolution of hydrogen gas at the cathode by adding, to the electrodepositable composition, a compound which is reduced by the hydrogen produced at the cathode during the electrodeposition. The hydrogen reacts with this non-gaseous compound rather than becoming hydrogen gas and forming bubbles which lead to pinhole defects.

FIELD OF THE INVENTION

This invention is related to my U.S. Pat. No. 4,592,816, entitledElectrophoretic Deposition Process, and my U.S. Pat. No. 4,877,818,entitled Electrophoretically Depositable Photosensitive PolymerComposition.

This invention relates to a method of reducing or eliminating defects inpolymeric films which are cataphoretically deposited onto conductivesurfaces from an aqueous medium. More particularly, this inventionrelates to the use of certain hydrogen scavenger compounds which reactwith hydrogen gas that evolves at the cathode during electrodepositionfrom an aqueous medium.

BACKGROUND OF THE INVENTION

Electrodeposition of polymeric films from aqueous dispersions ontoconductive surfaces is an attractive method for producing adherent filmsof uniform thickness. My U.S. Pat. No. 4,592,816 describes such aprocess for electrodepositing a photosensitive film which can be used asa aqueously developable, negative acting photoresist to transfer animage pattern onto a conductive surface such as a printed circuit board.The photosensitive composition used in my prior invention is an aqueousdispersion containing at least one polymer free of ethylenicunsaturation and having charged carrier groups, a photoinitiator and anunsaturated crosslinking monomer. The electrodeposited photosensitivefilm can be selectively exposed to a source of actinic radiation tocreate a crosslinked polymer image on the surface corresponding to theimage pattern described on a photomask, while the unexposed portion canbe removed from the surface using an aqueous developer solution. Anydefect, however small, such as for example a pinhole, in the imaged filmcan leave the conductive surface exposed and result in an incompletecircuit.

Electrodeposition of polymers (electrophoretic coating) generallyproduces good quality films of uniform thickness. The self limitingnature of the process assures that all conductive surfaces are coatedwith an even thickness of the film. In principal, this process producesfilms free of pinholes. A pinhole in the film leaves the conductivesurface of the substrate exposed, allowing the passage of current whichwould initiate the deposition of material in the pinhole. In practice,however, pinholes are observed in films applied by electrodeposition.

The coalescence of the emulsion particles into a film on the conductivesurface depends on hydroxide ions produced at the cathode surface by theelectrolysis of water. Hydrogen evolution is also a product of theelectrolysis of water occurring during the electrodeposition and canlead to pinholes in the film deposited by cationic electrodeposition(cataphoretic coating).

The emulsion particles in most emulsions for cationic electrodepositionare stabilized by the presence of protonated amines on the surface ofthe particle. These form a hydrophilic shell around the hydrophobicinterior of the stabilized particles in the aqueous matrix. The low pHof the bath keeps the amines protonated. During the electrodeposition,these charged particles migrate to the surface of the cathode under theinfluence of the potential applied across the electrodes. The pH at thecathode surface is much higher than the pH of the bulk of the emulsiondue to the hydroxide ions produced during the electrolysis of the water.The protonated amines are deprotonated and the particle becomeshydrophobic. The emulsion particle is no longer stable in the aqueousmedium because the hydrophilic shell of protonated amines has beendestroyed. These deprotonated particles coalesce to form a film on thesurface of the cathode.

The hydrogen, a product of the electrolysis of water, is necessary toimplement the electrodeposition of the polymer. Eliminating theelectrolysis of water would eliminate the hydrogen bubbles which producepinholes, but the polymer film would not be electrodeposited since nohydroxide would be produced.

The hydrogen gas produced at the cathode can produce defects at variousstages of the film formation. A hydrogen bubble formed on the surface ofthe substrate before the film has begun to deposit displaces theemulsion and prevents deposition in the area covered by the bubble. Thisresults in a pinhole in the final film. A bubble can also form under thefilm after the film deposition has started. This bubble can grow,lifting the film from the surface of the substrate (cathode), forming avoid under the thin layer film. No further deposition takes place sincethe bubble has excluded the emulsion and acts as an electricalinsulator. This can occur before the film has reached its fullthickness. The final film suffers voids covered with only a thin film ofthe polymeric material. These defects are unsightly and reduce theprotection provided electrodeposited coating. The thin film over thevoid can also break on drying or baking to produce a pinhole.

The problem of pinholes is usually addressed by formulating compositionsused to form a film which lead to few pinholes. However, few principlesare known for the formulation of compositions producing few pinholes,and trial and error is usually used. The deposition conditions can alsobe optimized to produce the fewest pinholes. Pinholes in the film can beeliminated by baking the film. This softens the film so that it flowsinto the pinholes.

Japanese Patent 56069836-A describes the use of unsaturated compounds toabsorb hydrogen gas during the electrodeposition of a glass dispersiononto a silicon surface to prevent pinholes in coating. This Japanesepatent describes only the use of unsaturated compounds with electronwithdrawing groups attached to the alpha position, such as acrylic acidand its esters, methacrylic acid and its esters, acrylonitrile, andstyrene. The electrodeposition was carried out at high voltages (450 V).No example of depositing an organic film is given. The compoundsdescribed in this Japanese patent showed little or no utility foreliminating hydrogen evolution in the deposition of organic films fromemulsions.

The reduction of compounds with hydrogen in the presence of a catalyst,known as catalytic hydrogenation, is well known and widely used.Catalytic hydrogenation is usually carried out by sealing hydrogen gas,the compound to be reduced and the catalyst in a vessel. The reactionmixture is agitated until the reaction is complete. Heat and pressureare frequently needed to complete the reaction in a reasonable amount oftime. Noble metals (and compounds of noble metals) are generally themost effective catalysts although base metals are also used. Thecatalyst is necessary because the addition of the hydrogen to thecompound does not take place directly. The hydrogen is first adsorbedonto the surface of the catalyst, and it is this adsorbed hydrogen thatreduces the compound.

A similar technique for reducing compounds that has received much lessattention is electrocatalytic hydrogenation (electrohydrogenation).Usually, the catalyst in this technique also acts as a cathode in anelectrolytic cell. In some cases the catalyst is coated onto a cathodewhich is not catalytic. The hydrogen produced by the electrolysis isadsorbed onto the catalyst surface. Reducible compounds dissolved in theelectrolyte are then reduced by the hydrogen adsorbed on the surface ofthe cathode/catalyst. The objective of electrocatalytic hydrogenation isto prepare the reduced product. The process of the present inventionuses a similar technique but the objective is to consume the hydrogenbefore it forms gas bubbles which cause defects in the film duringelectrodeposition.

It is the object of the present invention to eliminate or reduce thepinhole defects in cataphoretically deposited films. It is a furtherobject of the present invention to incorporate a compound into acataphoretically deposited photosensitive composition to decreasehydrogen gas evolution without interfering with the cataphoreticallydeposited films.

SUMMARY OF THE INVENTION

I have discovered a method for eliminating or reducing pinhole defectsin cataphoretically deposited films without interfering with theelectrolysis of water needed for electrodeposition. This methodcomprises decreasing the evolution of hydrogen gas at the cathode byadding a compound to the emulsion. This compound is reduced by thehydrogen produced at the cathode during the electrodeposition. Thehydrogen reacts with the this non-gaseous compound rather than becominghydrogen gas and forming bubbles which lead to pinhole defects.

DETAILED DESCRIPTION OF THE INVENTION

Decreasing hydrogen evolution at the cathode during cationicelectrodeposition is implemented by adding a "hydrogen scavenger" to theelectrodeposition emulsion before the electrodeposition is carried out.As used herein, "hydrogen scavenger" is any compound that reacts withhydrogen to prevent the formation of bubbles of gaseous hydrogen.

Although the mechanism of the process set forth herein is not fullyunderstood, it is believed the hydrogen scavenger reacts with thehydrogen in the following manner. The electrolysis produces hydrogenthat is adsorbed (or becomes adsorbed) on the surface of the metalcathode. This adsorbed hydrogen reacts with the hydrogen scavenger toproduce a reduced form of the hydrogen scavenger. This reduced hydrogenscavenger can be incorporated into the film or dissolved in the aqueousphase. It is also possible the reduced form dissolved in the aqueousphase can find its way to the anode and reoxidize to the originalhydrogen scavenger. In this case, no net consumption of the hydrogenscavenger takes place. The theory of this invention is presented here asa possible explanation of the results obtained and in no way is intendedto limit the scope of this invention.

Electrohydrogenation usually requires carefully prepared cathodes ofexpensive materials (e.g. platinum and rhodium) and high pressures arefrequently required to produce the proper efficiency. In order for thistechnique to be practical in the present process, the hydrogen scavengermust be effective under the conditions of the deposition cell(atmospheric pressure and temperatures below 50° C. are normally used).The metal of the article to be coated must act as an effective catalystsince special preparation would be impractical.

Two methods were used to evaluate candidate compounds to determine whichwere the most effective in decreasing the hydrogen gas production. Inthe first method, the evolution of hydrogen at the cathode in an aqueouselectrolyte is compared to the evolution after the compound beingevaluated has been added to the electrolyte. A decrease in the hydrogenevolution after the compound has been added indicates that it is capableof decreasing hydrogen evolution. The second test method is a functionaltest. A film is deposited by electrodeposition under conditions whichproduce pinholes due to hydrogen evolution. The compound being evaluatedas a hydrogen scavenger is then added to the emulsion. A secondelectrodeposition is then carried out. If this film has fewer defectsthan the film deposited before the compound was added then the compoundunder question is an effective hydrogen scavenger.

A number of compounds that work well as hydrogen scavengers have beenidentified. The more preferred compounds effective as hydrogenscavengers are organic nitro compounds and furans. Nitro compounds areknown to be readily reduced by catalytic hydrogenation. Organiccompounds that are soluble in the aqueous phase of the electrodepositionemulsion are preferred.

Preferred hydrogen scavengers are compounds that are readily reducedunder the conditions (temperature, pressure, pH, etc.) of theelectrodeposition and are not detrimental to the deposition process. Theby-products of the deposition should also not interfere with thedeposition. They should reduce the amount of hydrogen evolution at thecathode as evaluated by the electrolysis of an aqueous solution andshould be effective in a functional test.

Compounds effective as hydrogen scavengers are nitro compounds of thefollowing structure: ##STR1## wherein R₁ is hydrogen, or a C₁ -C₁₀ alkylgroup;

R₂ is hydrogen, a C₁ -C₁₀ alkyl group, an aromatic hydrocarbon group orhydroxyl substituted C₁ -C₁₀ alkyl group; and

R₃ is hydrogen, a C₁ -C₁₀ alkyl group, an aromatic hydrocarbon group, ora hydroxyl substituted C₁ -C₁₀ alkyl group; and

when R₁ and R₂ are both hydrogen, R₃ is hydrogen, a C₁ -C₁₀ alkyl group,an aromatic hydrocarbon group, or a hydroxyl substituted C₁ -C₁₀ alkylgroup;

when R₁ is hydrogen and R₂ is a C₁ -C₁₀ alkyl group or an aromatichydrocarbon group, R₃ is a C₁ -C₁₀ alkyl group, an aromatic hydrocarbongroup, or a hydroxyl substituted C₂ -C₁₀ alkyl group;

when R₁ is hydrogen and R₂ is a hydroxyl substituted C₁ -C₁₀ alkylgroup, R₃ is a hydroxyl substituted C₁ -C₁₀ alkyl group;

and when R₁ is a C₁ -C₁₀ alkyl group and R₂ is a C₁ -C₁₀ alkyl group ora hydroxyl substituted C₁ -C₁₀ alkyl group, R₃ is a hydroxyl substitutedC₁ -C₁₀ alkyl group.

Also useful as hydrogen scavengers are nitrobenzene, nitrobenzenesubstituted with hydroxyl groups, C₁ -C₁₀ alkyl groups, or hydroxylsubstituted C₁ -C₁₀ alkyl groups; furan and furan substituted withhydroxyl groups, C₁ -C₁₀ alkyl groups, or hydroxyl substituted C₁ -C₁₀alkyl groups.

The more preferred compounds are the compounds of structure I where R₁and R₂ are hydrogen, and R₃ is hydrogen, a C₁ -C₁₀ alkyl group or anhydroxyl substituted C₁ -C₁₀ alkyl group;

or where R₁ is hydrogen, R₂ is a C₁ -C₁₀ alkyl group, and R₃ is a C₁-C₁₀ alkyl group, or an hydroxyl substituted C₂ -C₁₀ alkyl group;

or where R₁ is hydrogen, and R₂ and R₃ are hydroxyl substituted C₁ -C₁₀alkyl groups;

or where R₁ is a C₁ -C₁₀ alkyl group, and R₂ and R₃ are hydroxylsubstituted C₁ -C₁₀ alkyl groups; and

nitrobenzene, and nitrobenzene substituted with hydroxyl groups, C₁ -C₁₀alkyl groups, or hydroxyl substituted C₁ -C₁₀ alkyl groups.

The most preferred hydrogen scavengers are nitromethane, nitroethane,1-nitropropane, 2-nitropropane, 2-nitroethanol, 2-nitro-1-propanol,3-nitro-2-butanol, 2-methyl-2-nitro-1-propanol, and 4-nitrobenzylalcohol.

The hydrogen scavenger is added to the emulsion or aqueous solution in aconcentration of from about 0.05% to 10% and more preferably from about3% to 5% by weight based on the total weight of the emulsion orsolution.

The polymeric films formed using the process of the present inventionare useful in such applications as the preparation of printed circuitboards, lithographic printing plates, and cathode ray tubes, as well asin chemical milling, solder resist, and planarizing layer applications.Additional uses for the polymeric films include electrodepositionapplications such as in the electrodeposition of undercoat paint forauto bodies and thermal or photocurable electrodeposition coatings forcans.

EXAMPLE 1 Evaluation of Hydrogen Scavengers by Electrolysis of anAqueous Solution

Compounds were evaluated for their capacity to reduce hydrogen evolutionat the cathode during electrolysis. Each compound was added to anelectrolyte and the amount of hydrogen gas produced at the cathode wasdetermined. Effective hydrogen scavengers will reduce the amount ofhydrogen evolved compared to the electrolysis of the electrolyte withoutadditives.

The electrolyte was a 0.10N HCl aq. solution. The electrodes (1×3.5 cm)were cut from metal foils and were mounted 4 cm apart in a cell,parallel and centered on one other. The cell was filled with 300 g. ofelectrolyte and a current of 200 mA was applied for 1.5 min. Thehydrogen that evolved from the cathode was collected in a graduatedcylinder and the volume determined. This was the amount of hydrogenevolved in the absence of the hydrogen scavenger.

To determine the effectiveness of a compound as a hydrogen scavenger, anelectrolyte was prepared from 300 g. of 0.10N HCl and 1.5 g of thecompound under evaluation. This was subjected to electrolysis in thecell described above to determine the amount of hydrogen evolved in thepresence of the compound under evaluation. An effective hydrogenscavenger is one that produces little hydrogen gas relative to theelectrolyte without the hydrogen scavenger. A copper cathode and astainless steel anode was used.

Each evaluation was carried out twice and the results averaged. Theresults are given in Table 1.

                  TABLE 1                                                         ______________________________________                                                           VOLUME                                                     COMPOUND           HYDROGEN GAS (ml)                                          ______________________________________                                        None               2.0                                                        3-Nitro-2-butanol  0.4                                                        2-Nitro-1-ethanol  0.4                                                        Tris(hydroxymethyl)nitromethane                                                                  1.0                                                        2-Ethyl-2-nitro-1,3-propanediol                                                                  0.7                                                        2-Methyl-2-nitro-1-propanol                                                                      0.6                                                        Nitromethane       0.1                                                        Nitroethane        0.3                                                        2-nitropropane     0.4                                                        4-nitrobenzyl alcohol.sup.1                                                                      0.8                                                        2-nitro-1-butanol  1.9                                                        Maleic acid        1.3                                                        1,4-but-2-ynediol.sup.1                                                                          1.8                                                        Acetonitrile       1.8                                                        Furfuryl alcohol.sup.1                                                                           1.0                                                        Hydroquinone       2.0                                                        Acetone            1.9                                                        Acrylic acid       1.5                                                        Itaconic acid      2.0                                                        Ethyl acrylate     1.5                                                        Methyl methacrylate                                                                              1.8                                                        2-bromo-2-nitro-1,3-propanediol                                                                  1.1                                                        3-nitro-1,2,4-triazole.sup.2                                                                     0.5                                                        Benzoquinone.sup.1 1.2                                                        Acrylamide         1.4                                                        2-Propanol         2.1                                                        Butyl lactate      2.2                                                        Acetic acid        2.1                                                        ______________________________________                                         .sup.1 The material did not completely dissolve in the electrolyte.           .sup.2 Evaluation was carried out using 150 g of 0.10N HCl and 0.75 g of      material.                                                                     The graduated cylinder used to collect the hydrogen gas was lowered to        accomodate the volume change.                                            

The results shown in Table 1 show that some materials substantiallyreduce the hydrogen evolution at the cathode while others haveessentially no effect.

EXAMPLE 2 Effect of Hydrogen Scavenger Concentration

The effect of concentration was determined by measuring the amount ofhydrogen produced at various levels of hydrogen scavenger. Nitromethanewas used as the hydrogen scavenger and 300 g of 0.10N HCl electrolytewas used in each case. The electrolysis was carried out as describedabove.

The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        WEIGHT OF       VOLUME OF                                                     NITROMETHANE (g)                                                                              HYDROGEN GAS (ml)                                             ______________________________________                                        0.0             2.1                                                           0.15            1.4                                                           0.30            1.1                                                           0.45            0.9                                                           0.75            0.4                                                           1.05            0.3                                                           1.50            0.1                                                           3.0             0.0                                                           12.0            0.0                                                           30.0            0.0                                                           ______________________________________                                    

These results show the hydrogen scavenger can reduce the amount ofhydrogen evolution even at concentrations as low as about 0.05%. Theeffectiveness increases as the concentration of the hydrogen scavengerincreases, until essentially no hydrogen is evolved. Concentrations ashigh as about 10% can be used.

EXAMPLE 3 Effect of Cathode Material on the Hydrogen Scavenger

Other metals were used as the cathode materials to show the influence ofthe cathode material on hydrogen evolution. The hydrogen evolution wasdetermined for each cathode material in 0.10N HCl in the absence of ahydrogen scavenger and in then in the presence of the hydrogenscavenger. The hydrogen scavenger in this evaluation was 0.5% by weightof 2-nitroethanol. The evaluation was carried out twice and the resultsaveraged.

The results are tabulated in Table 3.

                  TABLE 3                                                         ______________________________________                                                      HYDROGEN EVOLUTION                                                              WITHOUT      WITH                                                             HYDROGEN     HYDROGEN                                         CATHODE MATERIAL                                                                              SCAVENGER    SCAVENGER                                        ______________________________________                                        Copper          2.1          0.4                                              Aluminum        2.2          0.2                                              Graphite        2.2          0.2                                              Nickel          2.2          0.4                                              Stainless Steel 2.2          0.4                                              Zinc            2.2          0.2                                              Tin             2.2          0.3                                              Iron            2.2          0.3                                              Platinum        2.1          0.3                                              ______________________________________                                    

The results in Table 3 show that hydrogen evolution is reducedsubstantially for a wide variety of cathode materials.

EXAMPLE 4 Evaluation of Hydrogen Scavengers During Electrodeposition ofa Photocuring Film

Compounds were evaluated as hydrogen scavengers by a second method. Inthis evaluation, the compound was added to an electrodeposition emulsionwhich, under the conditions selected here, produces a film with defectsdue to hydrogen gas evolution. This method evaluates the effectivenessof the hydrogen scavenger under more realistic conditions but suffersfrom a drawback. The hydrogen scavenger can plasticize the emulsionparticles in such a way as to produce a thinner film. A thinner filmusually has fewer pinholes, even if the compound is ineffective as ahydrogen scavenger. A plasticizer with no capacity as a hydrogenscavenger will produce thinner films with fewer pinholes when added tothe emulsion. Therefore, I have found it useful to compare the number ofdefects at comparable film thickness. The thickness of the film wasincreased by adjusting the temperature of the deposition.

The emulsion was prepared by mixing 330 g. of a solution polymer (8parts dimethylaminoethyl methacrylate, 84 parts methyl methacrylate, and7 parts butyl methacrylate, as a 50% solution in Propasol® P solvent, atrade mark of the Union Carbide Corporation), 35 g. of pentaerythritoltriacrylate (PETA), and a solution of 0.57 g. of Oil Blue N dye in 45 g.of acetone. The mixture was stirred into a homogeneous solution. Then,14 g. of a 19% lactic acid solution was added and mixed thoroughly.Water (1770 g.) was added slowly with stirring to produce an emulsion.PETA (21 g.) was added to the emulsion and was stirred overnight. Theadded PETA was completely absorbed by the emulsion particles. Theemulsion particle size was 76 nm.

Films were deposited from a sample of the emulsion without addedhydrogen scavenger and compared to films deposited from samples ofemulsion containing the compound under investigation. The number ofpinholes were counted to determine the effectiveness of the compound forreducing defects in the film.

The anode for the electrodeposition was stainless steel with a surfacemeasuring 2.5×10 cm. The cathode material was copper clad circuit boardmaterial (0.017 cm thick copper foil clad to an epoxy composite base,total thickness 0.079 cm) measuring 2.5×10 cm. The copper surface of thecathode was cleaned with a pumice cleaner (Scrub Cleaner 11, ShipleyCompany) just before use. The emulsion (50 g.) was placed in a 100 mlbeaker. The electrodes, placed 2.5 cm apart with the surfaces paralleland centered, were immersed in the emulsion 3 cm. The emulsiontemperature was adjusted to 19° C. A potential of 100 V was applied for12 seconds.

The cathode was removed and rinsed with water and dried with a stream ofnitrogen. The film was then crosslinked by exposing it to ultravioletlight (Blakray model XX15 long wave ultraviolet light) for 3 minutes.

The film was evaluated for film defects by counting the defects inselected areas of the film. A mask, the size of the cathode, wasprepared for this evaluation. The mask had four holes measuring 2.5 mm.Two of the holes were 1.5 cm from the bottom of the mask and 2 mm infrom each edge, and the other two holes were centered along the lengthof the mask, one 1 cm from the bottom and one 2 cm from the bottom. Themask was placed on the coated cathode and the number of defects in theareas exposed by the holes was counted under a microscope and recorded.The number was sometimes estimated when about 25 or more defects werepresent. The number of defects will generally be higher near the edgesof the film than near the center of the film due to the higher currentdensity at the edges.

Hydrogen scavengers were evaluated by adding 0.25 g. of the material tobe evaluated to 50 g. of emulsion, stirring for 1 hour, depositing thefilm on a cathode, and evaluating as described above. An effectivehydrogen scavenger will reduce the number of defects caused by hydrogenevolution.

As stated above, the hydrogen scavenger under evaluation can act as aplasticizer and (in this case) cause thinner films to be deposited withfewer pinholes. The plasticization alone can lead to fewer defects.Therefore, the temperature of the emulsion during deposition wasdecreased to form a film of about the same thickness as the filmdeposited at 19° C. without the hydrogen scavenger.

The hydrogen scavenger, the temperature of deposition, and the number ofpinholes are recorded in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                    TEMP                                                                              THICKNESS                                                                             NUMBER OF PINHOLES                                HYDROGEN SCAVENGER                                                                            (°C.)                                                                      (m)     RIGHT                                                                              LEFT                                                                              TOP BOTTOM                               __________________________________________________________________________    None            19  34      19   19  7   8                                    3-Nitro-2-butanol                                                                             19  29      0    0   0   0                                    2-Nitro-1-ethanol                                                                             19  31      0    0   0   0                                    Tris(hydroxymethyl)nitromethane                                                               19  31      ˜70                                                                          ˜75                                                                         ˜50                                                                         ˜50                            2-Ethyl-2-nitro-1,3-propanediol                                                               19  36      10   7   1   1                                    2-Methyl-2-nitro-1-propanol                                                                   19  35      1    0   0   0                                    Nitromethane    19  26      0    0   0   0                                    Nitromethane    16  43      5    3   3   1                                    Nitroethane     19  24      0    0   0   0                                    Nitroethane     16  39      3    6   0   1                                    2-nitropropane  19  20      0    0   1   0                                    2-nitropropane  16  34      1    4   0   0                                    4-nitrobenzyl alcohol                                                                         19  20      1    0   0   1                                    4-nitrobenzyl alcohol                                                                         16  31      1    0   0   2                                    2-nitro-1-butanol                                                                             19  32      ˜60                                                                          ˜70                                                                         ˜50                                                                         ˜50                            Maleic acid     19  20      ˜60                                                                          ˜60                                                                         ˜30                                                                         ˜30                            Maleic acid     16  35      15   16  11  12                                   1,4-but-2-ynediol                                                                             19  33      ˜40                                                                          ˜40                                                                         15  18                                   Acetonitrile    19  35      11   16  5   6                                    Furfuryl alcohol                                                                              19  26      9    5   1   5                                    Hydroquinone    16  56      17   16  11  12                                   Acetone         19  27      2    0   4   0                                    Acetone         16  43      15   9   6   6                                    Acrylic acid    19   8      ˜100                                                                         ˜80                                                                         ˜80                                                                         ˜80                            Acrylic acid    16  13      ˜30                                                                          ˜30                                                                         11  15                                   Itaconic acid   19  18      ˜25                                                                          ˜25                                                                         ˜25                                                                         20                                   Itaconic acid   16  40      ˜50                                                                          ˜50                                                                         8   9                                    Ethyl acrylate  19  20      0    0   0   0                                    Ethyl acrylate  15  38      10   17  5   3                                    Methyl methacrylate                                                                           19  19      0    1   0   0                                    Methyl methacrylate                                                                           15  39      5    11  4   12                                   2-bromo-2-nitro-1,3-propanediol                                                               19  20      4    8   9   6                                    2-bromo-2-nitro-1,3-propanediol                                                               16  38      18   12  19  9                                    3-nitro-1,2,4-triazole                                                                        19  38      ˜100                                                                         ˜100                                                                        ˜100                                                                        ˜100                           Benzoquinone    19  25      2    0   1   0                                    Benzoquinone    16  35      11   5   3   1                                    Acrylamide      19  40      16   18  6   11                                   2-Propanol      19  37      13   15  6   11                                   Butyl lactate   19  20      1    19  1   2                                    Butyl lactate   16  38      13   18  7   6                                    Acetic acid     19   6      ˜100                                                                         ˜100                                                                        13  26                                   Acetic acid     16  36      ˜100                                                                         ˜100                                                                        ˜50                                                                         ˜50                            __________________________________________________________________________

EXAMPLE 5 Effect of Hydrogen Scavenger Concentration in anElectrodeposition Coating Emulsion

The effect of hydrogen scavenger concentration was evaluated bydepositing film from an emulsion containing various concentrations of2-nitroethanol. The depositions were carried out as described in Example4. The number of defects was determined as described above and theresults are tabulated in Table 5.

                  TABLE 5                                                         ______________________________________                                        2-NITRO- THICK-                                                               ETHANOL  NESS                                                                 CONC (%) (m)      RIGHT    LEFT  TOP   BOTTOM                                 ______________________________________                                        0        42       14       13    7     9                                      0.10     39       14       14    15    11                                     0.15     40       6        16    2     7                                      0.20     37       4        10    3     3                                      0.40     36       1         3    1     1                                      1.0      20       0         2    0     0                                      5.0       6       0         0    2     2                                      5.0*     23       1         0    2     2                                      ______________________________________                                         *Deposited at 10° C. to produce at thicker film.                  

These results show the hydrogen scavenger is effective in concentrationsas low a 0.15% and as high as 5% in the coating emulsion.

EXAMPLE 6 Effect of Cathode Material on the Effectiveness of theHydrogen Scavenger During Film Deposition

The effectiveness of the hydrogen scavenger was determined when filmswere deposited onto a variety of metals. Films were deposited from 50 g.of emulsion, with or without the hydrogen scavenger, onto foils ofdifferent metals. The evaluation was carried out as described in Example4. The results are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                        2-NITRO-                                                                      ETHANOL                                                                       CATHODE                                                                       MATERIAL (g)    RIGHT     LEFT  TOP   BOTTOM                                  ______________________________________                                        Stainless steel                                                                        0      >100      >100  ˜80                                                                           ˜80                               Stainless steel                                                                        0.5    17        9     7     11                                      Iron     0      12        23    4     5                                       Iron     0.5    0         3     0     1                                       Zinc     0      >100      >100  >100  >100                                    Zinc     0.5    17        28    5     23                                      Graphite 0      >100      >100  >100  >100                                    Graphite 0.5    >100      >100  >100  >100                                    Aluminum 0      >100      >100  >100  >100                                    Aluminum 0.5    >100      >100  >100  >100                                    Nickel   0      32        30    13    13                                      Nickel   0.25   0         0     0     1                                       Tin      0      ˜80 ˜80                                                                           ˜80                                                                           ˜80                               Tin      0.5    ˜60 ˜60                                                                           ˜60                                                                           ˜60                               Platinum 0      >100      >100  >100  >100                                    Platinum 0.5    >100      17    ˜50                                                                           >100                                    ______________________________________                                    

These results in Table 6 show the hydrogen scavenger reduces the defectson a variety of cathode materials. Some of the cathode materials thatshowed very high defect counts were not substantially improved by thehydrogen scavenger. These defects may have been caused by a mechanismother than hydrogen evolution. Such defects are not eliminated by thehydrogen scavenger.

EXAMPLE 7 Effect of Hydrogen Scavenger on the Electrodeposition of aNoncuring Film From an Emulsion

An emulsion was prepared which produced a film that was not aphotoresist. The purpose was to demonstrate that the hydrogen evolutioncan be reduced using emulsions of conventional coatings.

The emulsion was prepared by mixing 16.9 g. of a solution polymer (3.5parts dimethylaminoethyl methacrylate, 68 parts methyl methacrylate, and28.5 parts butyl methacrylate, as a 60% solution in Propasol® P solvent)and a solution of 0.027 g. of Oil Blue N dye in 3.0 g. of acetone. Themixture was stirred into a homogeneous solution. Then, 1.0 g. of a 19%lactic acid solution was added and mixed thoroughly. Water (79 g.) wasadded slowly, with stirring, to produce an emulsion.

The emulsion was divided into two 50 g. samples and 2-nitroethanol (0.25g) was added to one of the emulsion samples. Films were deposited ontocopper clad circuit board substrates, as described in Example 4, at 29°C. The number of defects were then determined for the film from eachemulsion and are shown in Table 7.

                  TABLE 7                                                         ______________________________________                                                  THICK-                                                                        NESS                                                                EMULSION  (m)      RIGHT    LEFT  TOP  BOTTOM                                 ______________________________________                                        Without   23       10       8     4    6                                      2-nitropropanol                                                               With      23        3       3     0    1                                      2-nitropropanol                                                               ______________________________________                                    

These results in Table 7 show the hydrogen scavengers are effective forreducing the number of defects in conventional coatings.

I claim:
 1. A process for reducing pinhole defects in cataphoreticallydeposited films comprising electrophoretically depositing on a surface afilm formed from a polymer composition comprising an aqueous solution oremulsion of at least one polymer and a compound reduced by hydrogenproduced during said deposition.
 2. The process of claim 1 wherein saidpolymer composition further comprises a photoinitiator and anunsaturated crosslinking monomer.
 3. The process of claim 1 wherein saidcompound reduced by hydrogen is selected from the group consisting of;compounds characterized by the formula. ##STR2## wherein R₁ is hydrogen,or a C₁ -C₁₀ alkyl group, R₂ is hydrogen, a C₁ -C₁₀ alkyl group, anaromatic hydrocarbon group or hydroxyl substituted C₁ -C₁₀ alkyl groupand R₃ is hydrogen, a C₁ -C₁₀ alkyl group, an aromatic hydrocarbongroup, or a hydroxyl substituted C₁ -C₁₀ alkyl group and when R₁ and R₂are both hydrogen, R₃ is hydrogen, a C₁ -C₁₀ alkyl group, an aromatichydrocarbon group, or a hydroxyl substituted C₁ -C₁₀ alkyl group, whenR₁ is hydrogen and R₂ is a C₁ -C₁₀ alkyl group or an aromatichydrocarbon group, R₃ is a C₁ -C₁₀ alkyl group, an aromatic hydrocarbongroup, or a hydroxyl substituted C₂ -C₁₀ alkyl group, when R₁ ishydrogen and R₂ is a hydroxyl substituted C₁ -C₁₀ alkyl group, R₃ is ahydroxyl substituted C₁ -C₁₀ alkyl group, when R₁ is a C₁ -C₁₀ alkylgroup and R₂ is a C₁ -C₁₀ alkyl group or a hydroxyl substituted C₁ -C₁₀alkyl group, R₃ is a hydroxyl substituted C₁ -C₁₀ alkyl group;nitrobenzene, nitrobenzene substituted with hydroxyl groups, C₁ -C₁₀alkyl groups, or hydroxyl substituted C₁ -C₁₀ alkyl groups, furan andfuran substituted with hydroxyl groups, C₁ -C₁₀ alkyl groups, orhydroxyl substituted C₁ -C₁₀ alkyl groups.
 4. The process of claim 1wherein said compound reduced by hydrogen is selected from the groupconsisting of nitromethane, nitroethane, 1-nitropropane, 2-nitropropane,2-nitroethanol, 2-nitro-1-propanol, 3-nitro-2-butanol,2-methyl-2-nitro-1-propanol, and 4-nitrobenzyl alcohol.
 5. The processof claim 1 wherein said compound reduced by hydrogen is at aconcentration of from about 0.05% to 10% by weight based on the totalweight of said composition.
 6. The process of claim 1 wherein saidcompound reduced by hydrogen is at a concentration of from about 3% to5% by weight based on the total weight of said composition.